CN104384283A - Hot-stamping forming process of 22MnB5 high-strength thin steel plate - Google Patents

Abstract

The invention discloses a hot-stamping forming process of a 22MnB5 high-strength thin steel plate. The process comprises the following steps of processing the 22MnB5 high-strength thin steel plate to form a plate material of which the plate thickness is 1.5-2.0mm; putting the plate material into a resistance heating furnace, heating the plate material until the temperature of the plate material is 920-970 DEG C, and maintaining the temperature for 4-10min; transferring the plate material to a mold of which a friction coefficient is 0.20-0.40, and performing hot stamping, wherein the initial forming temperature of the plate material is controlled to be 750-950 DEG C, the transfer time is 3-8s, and the stamping speed is 20-40mm/s; continuously feeding cooling water into the mold in the whole hot-stamping process, and performing strong wind cooling, wherein the temperature of the cooling water is equal to room temperature namely 20 DEG C; continuously cooling the plate material in the mold, maintaining pressure for 2-10s, and then finishing pressure maintaining. After hot-stamping forming, the plate material is high in part strength, high in hardness, high in dimensional accuracy, smaller in resilience force, high in safety and long in service life; moreover, the maximum tensile strength can reach 1,500MPa.

Description

A hot stamping forming process of 22MnB5 high-strength thin steel plate

technical field

The invention belongs to the technical field of hot stamping technology, and in particular relates to a hot stamping forming technology of 22MnB5 high-strength thin steel plate.

Background technique

High-strength steel parts can greatly reduce vehicle weight while improving safety performance such as anti-collision, reduce fuel consumption and reduce exhaust pollution to the environment, so they have broad application prospects in automotive body structural parts and safety parts. High-strength steel has unparalleled ultra-high strength and hardness, but its hardening index and elongation are relatively low, which seriously affects its formability at room temperature. High-strength steel formed at room temperature is prone to various defects due to poor material fluidity, such as cracks, wrinkles, and unstable parts size and shape caused by springback. The poor size and shape stability of parts caused by springback is the most serious problem in the forming of high-strength steel plates. At the same time, due to its ultra-high strength and hardness, the stamping pressure is greatly increased, which undoubtedly increases the production cost.

22MnB5 is low carbon boron steel, its chemical composition is: C0.22～0.25, Mn1.20～1.40, Si0.20～0.30, Al0.02～0.05, B0.002～0.0035, Cr0.11～0.20, Ti0 .02～0.05, Mo0～0.10, Cu0～0.10, Ni0～0.10, Fe balance. It contains a very small amount of boron, which can greatly reduce the critical cooling rate for obtaining martensitic structure. It is a high-strength steel that is widely used in hot stamping parts for automobiles. The 22MnB5 high-strength steel plate adds trace boron elements on the basis of carbon-manganese steel. The main function is to improve the hardenability of the steel. martensitic capacity. The greater the depth of the martensite structure after quenching transformation, the higher the hardenability of the steel, and the more uniform the structure and properties. This is also the core issue of the hardenable boron steel in the hot stamping process.

The existing hot stamping forming technology only considers the mechanical properties after forming, and does not consider the thinning rate and maximum temperature difference of the sheet after forming. Due to the characteristics of stamping, some parts of the sheet are affected by force during the stamping The thickness is seriously thinned, and even the defect of cracking occurs. This phenomenon is more likely to occur in the stamping of thin-walled parts. The two index parameters, the thinning rate and the maximum temperature difference, determine the dimensional accuracy of the part after forming. Among them, the maximum The size of the temperature difference also determines the size of the internal stress of the part after forming, that is, determines the safety and service life of the part. Therefore, it is urgent to provide a new process to improve the tensile strength, safety and service life of parts.

Contents of the invention

The purpose of the present invention is to provide a 22MnB5 high-strength thin steel plate hot stamping forming process, thereby solving the problems existing in the background technology.

The technical problem solved by the present invention adopts following technical scheme to realize:

A 22MnB5 high-strength thin steel sheet hot stamping forming process, specifically comprising the following steps:

(1) Blanking: process the 22MnB5 high-strength steel plate into a blank, cut the blank into a sheet through a shearing machine, and drill a positioning hole according to the size of the mold;

(2) Heating and heat preservation: Put the sheet into a resistance heating furnace and heat it to 920-970°C, and keep it warm for 4-10 minutes to make the sheet evenly austenitized;

(3) Transfer stamping forming: Transfer the sheet to a mold with a friction coefficient of 0.20-0.40 for hot stamping. During the transfer process, the high-temperature sheet exchanges heat with the air, and the initial temperature of the sheet forming is controlled at 750-950°C. The transfer time is 3-8s, and the stamping speed is 20-40mm/s. During the whole hot stamping process, the mold is continuously fed with cooling water at a room temperature of 20°C, and at the same time, it is cooled by strong wind;

(4) Holding pressure and setting: After the hot stamping process is over, do not take out the sheet, wait for it to continue cooling in the mold, and finish the pressure holding after 2-10s.

The thickness of the sheet material processed from the 22MnB5 high-strength steel plate is 0.9-2.0mm.

Preferably, when the initial forming temperature of the sheet metal is 750°C, the stamping speed is 40mm/s, the holding time is 10s, and the friction coefficient is 0.20, the effect is the best. After the end, the temperature difference can slow down the thickness reduction at the same time, which can improve the mechanical properties and quality of the formed parts, and can improve production efficiency and reduce production costs.

Heating temperature and holding time will affect the hot stamping forming process and the quality of formed parts, so an appropriate temperature and holding time should be selected. The basis for selecting the austenitization temperature: first, the austenitization temperature of the steel plate is above the complete austenite structure, which provides conditions for the subsequent quenching to obtain martensite; the second is to choose the temperature at which the metal will undergo a strong oxidation reaction The following is to avoid defects caused by material oxidation; the third is to consider the heat loss in the subsequent blank transfer process. In order to ensure the forming start temperature, the selected heating temperature is 920-970 °C.

In order to achieve the purpose of obtaining more martensite structure after stamping and quenching, the billet must be heated and then kept warm to fully dissolve the residual cementite and obtain a uniform austenite structure. At the same time, since the original structure has a great influence on the quality of stamping parts, too long holding time will cause grain growth and reduce the quality of stamping parts, so the holding time is 4-10.

The sheet is quickly transferred from the heating furnace to the mold, and during the process of transferring the sheet from the heating furnace to the stamping die, due to contact with the air at 20°C, heat exchange will occur between the sheet and the air. In order to ensure that the sheet metal has good fluidity during the stamping forming process and obtain more martensitic structure during the quenching process, the initial temperature of stamping is guaranteed to be 750-950°C, and the heat loss of the sheet metal during the transfer process is very high. Large, so the transfer time should be shortened as much as possible, and the transfer time is 3-8s.

The friction coefficient of the mold is selected as 0.20-0.40, because the sheet metal is in a high temperature state during the hot stamping process, which puts forward higher requirements for the mold material and quality. The mold not only needs to have good thermal conductivity, but also to ensure high strength, high hardness and excellent fatigue resistance, and to be able to resist thermal friction in an alternating cold and hot environment without thermal cracks; at the same time, in order to reduce friction, the surface quality of the mold needs to be After strict control.

Because the cooling capacity of the mold is not enough, it will not only affect the strength of the formed part, but also cause thermal cracks of the mold caused by high temperature during the forming process, which will affect the dimensional accuracy of the part. In order to ensure the cooling rate of the sheet during the hot stamping process, the hot stamping die is equipped with cooling water pipes, which are located near the edge of the die, because during the hot stamping process, the high temperature sheet is in direct contact with the die, and the die absorbs heat As a result, the temperature rises and the cooling capacity of the mold is significantly reduced. Therefore, during the hot stamping process, the mold needs to be continuously fed with cooling water at a room temperature of 20°C to take away the heat absorbed by the contact between the mold and the sheet. It is difficult for hot stamping to achieve a high cooling rate only by cooling the mold, so strong wind is used to assist cooling, so as to significantly increase the cooling rate of the sheet.

The main advantage of the hot stamping process is that it can significantly improve the mechanical properties and quality accuracy of stamping parts. The temperature change of the sheet metal during the hot stamping process is a reflection of the quenching phase transition. However, in the actual hot stamping production process, due to the shape requirements of the part, the start time of contact between different parts and the mold is different, resulting in the temperature of the part after the holding pressure is completed. The difference is very large, which shows that the average cooling rate difference of each part of the part is large, and the degree of quenching is extremely uneven, which is not conducive to obtaining stamping parts with uniform structure and properties; and the uneven temperature distribution causes thermal stress inside the sheet, and the stress It will increase the springback of the parts and affect the dimensional accuracy of the stamping parts. Therefore, by selecting appropriate process parameters to control the temperature difference of the parts after the pressure holding is completed, the purpose of improving the uniformity of quenching and obtaining stamping parts with a more uniform structure distribution can be achieved.

The present invention has the following beneficial effects:

The parts prepared by the process of the present invention can be used for automobile A pillars, B pillars, reinforcement plates, structural beams, anti-collision beams and other parts. It shows excellent forming performance, high strength and high hardness, meets the requirements of automobile anti-collision performance, high dimensional accuracy, small rebound, high safety, long service life, and the maximum tensile strength can reach 1500MPa.

Detailed ways

In order to make the technical means, creative features, goals and effects achieved by the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

Example 1:

A 22MnB5 high-strength thin steel sheet hot stamping forming process, specifically comprising the following steps:

(1) Blanking: process 22MnB5 high-strength steel plate into a blank with a plate thickness of 0.9mm, cut the blank into a rectangular plate by a shearing machine, and drill positioning holes according to the mold size requirements;

(2) Heating and heat preservation: Put the sheet into a resistance heating furnace and heat it to 920°C, and keep it warm for 4 minutes to make the sheet evenly austenitized;

(3) Transfer stamping: Transfer the sheet to a mold with a friction coefficient of 0.25 for hot stamping. During the transfer process, the high-temperature sheet exchanges heat with the air. The initial temperature of sheet forming is controlled at 800°C, and the transfer time is 3s. , the stamping speed is 20/s, during the whole hot stamping process, the mold is continuously fed with cooling water at a room temperature of 20°C, and at the same time, it is cooled by strong wind;

(4): Holding pressure and setting: After the hot stamping process is over, do not take out the sheet, wait for it to continue cooling in the mold, and end the holding pressure after holding the pressure for 2 seconds.

Example 2:

A 22MnB5 high-strength thin steel sheet hot stamping forming process, specifically comprising the following steps:

(1) Blanking: process 22MnB5 high-strength steel plate into a blank with a plate thickness of 1.2 mm, cut the blank into a rectangular plate by a shearing machine, and drill positioning holes according to the mold size requirements;

(2) Heating and heat preservation: put the sheet into a resistance heating furnace and heat it to 930°C, and keep it warm for 6 minutes to make the sheet evenly austenitized;

(3) Transfer stamping forming: Transfer the sheet to a mold with a friction coefficient of 0.35 for hot stamping. During the transfer process, the high-temperature sheet exchanges heat with the air. The initial temperature of sheet forming is controlled at 900°C, and the transfer time is 4s. , the stamping speed is 25mm/s, during the whole hot stamping process, the mold is continuously fed with cooling water at a room temperature of 20°C, and at the same time, it is cooled by strong wind;

(4) Holding pressure and setting: After the hot stamping process is over, do not take out the sheet, wait for it to continue cooling in the mold, and end the holding pressure after holding the pressure for 4 seconds.

Example 3:

A 22MnB5 high-strength thin steel sheet hot stamping forming process, specifically comprising the following steps:

(1) Blanking: process 22MnB5 high-strength steel plate into a blank with a plate thickness of 1.8mm, cut the blank into a rectangular plate by a shearing machine, and drill positioning holes according to the mold size requirements;

(2) Heating and heat preservation: Put the sheet into a resistance heating furnace and heat it to 950°C, and keep it warm for 5 minutes to make the sheet evenly austenitized;

(3) Transfer stamping: Transfer the sheet to a mold with a friction coefficient of 0.20 for hot stamping. During the transfer process, the high-temperature sheet exchanges heat with the air. The initial temperature of sheet forming is controlled at 750°C, and the transfer time is 8s. , the stamping speed is 40mm/s, during the whole hot stamping process, the mold is continuously fed with cooling water at a room temperature of 20°C, and at the same time, it is cooled by strong wind;

(4) Holding pressure and setting: After the hot stamping process is completed, do not take out the sheet, wait for it to continue cooling in the mold, and end the holding pressure after holding the pressure for 10s.

Example 4:

A 22MnB5 high-strength thin steel sheet hot stamping forming process, specifically comprising the following steps:

(1) Blanking: process 22MnB5 high-strength steel plate into a blank with a plate thickness of 1.5mm, cut the blank into a rectangular plate by a shearing machine, and drill positioning holes according to the mold size requirements;

(2) Heating and heat preservation: Put the sheet into a resistance heating furnace and heat it to 960°C, and keep it warm for 8 minutes to make the sheet evenly austenitized;

(3) Transfer stamping forming: Transfer the sheet to a mold with a friction coefficient of 0.30 for hot stamping. During the transfer process, the high-temperature sheet exchanges heat with the air. The initial temperature of sheet forming is controlled at 850°C, and the transfer time is 5s. , the stamping speed is 30mm/s, during the whole hot stamping process, the mold is continuously fed with cooling water at a room temperature of 20°C, and at the same time, it is cooled by strong wind;

(4) Holding pressure and setting: After the hot stamping process is over, do not take out the sheet, wait for it to continue cooling in the mold, and finish the pressure holding after 6 seconds.

Example 5:

A 22MnB5 high-strength thin steel sheet hot stamping forming process, specifically comprising the following steps:

(1) Blanking: process 22MnB5 high-strength steel plate into a blank with a plate thickness of 2.0mm, cut the blank into a rectangular plate through a shearing machine, and drill positioning holes according to the mold size requirements;

(2) Heating and heat preservation: put the sheet into a resistance heating furnace and heat it to 970°C, and keep it warm for 10 minutes to make the sheet evenly austenitized;

(3) Transfer stamping forming: Transfer the sheet to a mold with a friction coefficient of 0.40 for hot stamping. During the transfer process, the high-temperature sheet exchanges heat with the air. The initial temperature of sheet forming is controlled at 950°C, and the transfer time is 6s. , the stamping speed is 35mm/s, during the whole hot stamping process, the mold is continuously fed with cooling water at a room temperature of 20°C, and at the same time, it is cooled by strong wind;

(4) Holding pressure and setting: After the hot stamping process is over, do not take out the sheet, wait for it to continue cooling in the mold, and end the holding pressure after holding the pressure for 8 seconds.

The parts prepared by the process of the present invention can be used for automobile A pillars, B pillars, reinforcement plates, structural beams, anti-collision beams and other parts. It shows excellent forming performance, high strength and high hardness, meets the requirements of automobile anti-collision performance, high dimensional accuracy, small rebound, high safety, long service life, and the maximum tensile strength can reach 1500MPa.

The optimal combination of process parameters is the initial temperature of sheet metal forming at 750°C, the stamping speed of 40mm/s, the holding time of 10s, and the friction coefficient of 0.20. This set of process parameters reduces the temperature difference after the hot stamping parts are pressed and at the same time slows down the thickness reduction. Improve the mechanical properties and quality of formed parts, and can improve production efficiency and reduce production costs. The high-strength steel 22MnB5 is selected, and the geometric model of the U-shaped part is established based on the typical characteristics of the B-pillar of the automobile structural parts. The maximum temperature difference and the maximum thinning rate of the part after the pressure-holding are used as the experimental indicators, and the thermal simulation test technology, orthogonal experimental design, numerical value The combination of simulation and experiment is used for verification, as shown in Table 1, the arrangement of the orthogonal experiment scheme and the simulation results.

Table 1

Experimental indicators The optimal combination of hot stamping process parameters for the maximum temperature difference of U-shaped parts after the pressure holding is completed is the holding time of 10s, the initial sheet forming temperature of 750°C, the stamping speed of 40mm/s, and the friction coefficient of 0.20; while the maximum thinning rate of U-shaped parts The optimal combination of hot stamping process parameters is friction coefficient 0.20, sheet metal forming initial temperature 750°C, holding time 4s, stamping speed 20mm/s. The order of the primary and secondary factors affecting the two factors and the selection of the optimal level are inconsistent. The specific analysis is as follows:

(1) The holding time is the main influencing factor in the maximum temperature difference of the U-shaped part after the end of the experimental index. When the holding pressure is selected for 10s, the maximum temperature difference of the U-shaped part after the holding pressure is reduced by 41.44 compared with the holding pressure of 4s. %, and the holding time is an insignificant factor in the evaluation index of the maximum thinning rate of U-shaped parts, and has little influence on the change of the maximum thinning rate, so the holding time is selected as 10s.

(2) For the two experimental indicators of the maximum temperature difference of the U-shaped part and the maximum thinning rate of the U-shaped part after the end of the pressure holding, the initial temperature of the sheet metal forming is a secondary influencing factor, and the optimal level of both is 750 °C, Therefore, the initial temperature of sheet metal forming is selected to be 750°C.

(3) The friction coefficient is the main influencing factor in the maximum thinning rate of the U-shaped part in the experimental index, while the friction coefficient is an insignificant factor in the evaluation index of the maximum temperature difference of the U-shaped part after the pressure holding is completed, and the change has a great influence on it. Small; comprehensively considering the wear of the mold and the surface quality and dimensional accuracy of the stamping parts, the excellent level obtained by the analysis of the two sets of data is consistent, that is, the friction coefficient is selected as 0.20.

(4) The stamping speed is not a significant factor in the two evaluation indicators of the maximum temperature difference and the maximum thinning rate of the U-shaped part after the pressure holding is completed, especially the change of the maximum thinning rate is very small, at 20-40mm/s Within the range of stamping speed, the thinning rate of U-shaped parts is less than 10%, about 6% to 7%, far less than the limit value of thinning rate of 30%, which can be considered as a stamping speed of 20 to 40mm/s Within the range, the maximum thinning rate has reached an optimal level. At the same time, considering the production efficiency, the stamping speed is selected as 40mm/s.

The basic principles and main features of the present invention and the advantages of the present invention have been shown and described above. Those skilled in the industry should understand that the present invention is not limited by the above-mentioned embodiments. What are described in the above-mentioned embodiments and the description only illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have Variations and improvements are possible, which fall within the scope of the claimed invention. The protection scope of the present invention is defined by the appended claims and their equivalents.

Claims (3)

1. the hot press-formed technique of 22MnB5 high-strength steel sheet, is characterized in that: specifically comprise the steps:

(1) blanking: 22MnB5 high-strength steel sheet is processed into blank, by plate shearing machine, blank is cut to plate, requires to get out locating hole according to die size;

(2) heating and thermal insulation: plate is put into resistance-heated furnace and is heated to 920-970 DEG C, insulation 4-10min, makes plate uniform austenitic;

(3) shift stamping: plate is transferred on mould that coefficient of friction is 0.20-0.40 and carries out drop stamping, in transfer process, high temperature plate and air carry out exchange heat, sheet forming initial temperature controls at 750-950 DEG C, transfer time is 3-8s, drawing velocity is 20-40mm/s, in whole hot stamping operation, mould does not stop to pass into the cooling water that temperature is room temperature 20 DEG C, imposes strong wind cooling simultaneously;

(4) pressurize setting: after hot stamping operation terminates, do not take out plate, treats that it continues cooling in a mold, terminates pressurize after pressurize 2-10s.

2. the hot press-formed technique of a kind of 22MnB5 high-strength steel sheet according to claim 1, is characterized in that: the plate thickness of slab that described 22MnB5 high-strength steel sheet is processed into is 0.9-2.0mm.

3. the hot press-formed technique of a kind of 22MnB5 high-strength steel sheet according to claim 1, it is characterized in that: described sheet forming initial temperature is 750 DEG C, drawing velocity is 40mm/s, and the dwell time is 10s, and coefficient of friction is 0.20.